A digital transmission system using an optical fiber is widely used in a wired communication area. An optical transmission system a time division multiplexing (TDM) scheme has been widely used. The TDM scheme transmits a high-speed signal by time-division multiplexing multiple signals for transferring data including voice data. For example, a representative system using the TDM technology includes a synchronous optical networking (SONET)/synchronous digital hierarchy (SDH) optical transmission system.
As demands for applications requiring advanced features and more data increase, an amount of non-voice data such as video, data, and the like has increased tremendously far exceeding that of regular voice traffic. Accordingly, in recent years, an optical transport network (OTN) type optical transmission system has been introduced and implemented with a high transmission speed, reaching up to a 100 Giga bits per second (Gbps) of bit rate. A basic type of an OTN type optical transmission system includes a TDM type transmission technology.
Alternatively, another type of transmission technology has been gaining popularity with increased data traffic, e.g., a wavelength division multiplexing (WDM) type based technology. The WDM type based technology greatly increases a transmission capacity of the optical communication system. WDM is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser light. For example, in a WDM based communication system, a wavelength band is divided into multiples of narrow wavelength bands and thereafter, a digital signal may be allocated and transmitted to a wavelength of each the narrow wavelength bands.
The WDM based technology is independent of a transmission speed of the digital signal, and thus has been widely used to construct a hundreds Gbps-grade large-capacity optical transmission system.
FIG. 1 illustrates an example of a general dense wavelength division multiplexing (DWDM) optical transmission network configuration, in which a central office 2 is connected to a core network 1. The central office 2 and respective local offices 3, 4, and 5 (e.g., base stations 3, 4, and 5) are generally arranged to form a ring-type network. The number of the local offices may vary depending on an actual implementation of the system configuration.
Let us assume that the respective base stations 3, 4, and 5 are configured to be connected with one or more remote sites or stations. By way of example, in FIG. 1, the base station 3 is configured to be connected with a remote site 6. FIG. 2 illustrates an example method for allocating a wavelength in configuring a link between the local office 3 and the remote site 6. In this configuration, transmission and reception wavelengths are different from each other and thus respective optical transceivers may perform transmission and reception in different wavelengths. For example, as shown in FIG. 2, the local office 3 includes a plurality of optical transceivers 11, 12, . . . , 13 and N (e.g., optical TRX 1, optical TRX2, . . . , optical TRX N) and the remote site 6 includes a plurality of optical transceivers 21, 22, . . . , and 23 (e.g., optical TRX 1′, optical TRX 2′, . . . , optical TRX N′). In the example, the local office 3 uses a set of transmission wavelengths λa, λb, . . . , and λn, and the remote site 6 may use a second set of transmission wavelengths λA, λB, . . . , and λN over a single optical fiber 9 (or also used as an optical link herein). As a result, the transmission and reception wavelengths of the respective optical transceivers in the local office 3 or remote site 6 different and may be in different wavelength bands arranged at different positions.
In another implementation, as shown in FIG. 3, both the local office 3 and the remote site 6 may use the same set of transmission wavelengths λa, λb, . . . , and λn. Accordingly, the transmission and reception wavelengths of the optical transceivers 11, 12, and 13 of the local office 3 and the optical transceivers 21, 22, and 23 of the remote site 6 are arranged at the same position, respectively. Such a configuration provides certain advantages, such as the reduced number of wavelengths and the increased number of channels over the single optical fiber 9, compared to the example configuration shown in FIG. 2.
However, in the example implementation shown in FIG. 3, since the wavelengths used in the configuration above between the local office 3 and the remote site 6 may be arranged close to each other (e.g., as in DWDM) noise and inter-wavelength interference may occur, thereby degrading the performance of the optical communication system. Further, a probability of having a transmission error may be increased as the transmission and reception wavelengths are changed due to external factors.
Accordingly, there is a need for an improved method for improving performance of an optical communication system in a DWDM system using a single optical fiber, in which wavelengths of an uplink signal and a downlink signal are close to each other due to the external factors.